A multi-junction photoelectric conversion device (multi-junction solar cell) in which a plurality of photoelectric conversion units are stacked in series is known. For example, Patent Document 1 discloses a multi-junction thin-film photoelectric conversion device in which an amorphous photoelectric conversion unit (top cell) including an amorphous silicon thin-film as a photoelectric conversion layer, and a photoelectric conversion unit (bottom cell) including a microcrystalline silicon thin-film as a photoelectric conversion layer are stacked. Patent Document 2 discloses a multi-junction photoelectric conversion device in which as a top cell, an amorphous silicon photoelectric conversion unit is stacked on the light-receiving side of a bottom cell including a crystalline silicon substrate. Patent Document 3 discloses a multi-junction photoelectric conversion device in which as a top cell, a perovskite photoelectric conversion unit is stacked on the light-receiving side of a bottom cell including a crystalline silicon substrate etc.
In a semiconductor thin-film that is used as a photoelectric conversion layer, generation of defects such as pinholes during deposition by chemical vapor deposition (CVD), sputtering, vacuum vapor deposition, solution coating, or the like is unavoidable, and these defects cause leakage between electrodes. A method is known in which for the purpose of eliminating leakage caused by pinholes or the like of a thin-film, a reverse bias voltage is applied between electrodes of a photoelectric conversion device to eliminate a leakage path. By application of a reverse bias voltage, current is concentrated on a leakage portion of a semiconductor thin-film, and therefore local generation of heat occurs, so that the leakage portion is insulated by oxidation or melting.
Defects such as pinholes during formation of a thin-film generate in random. For eliminating leakage by applying a reverse bias voltage to a semiconductor thin-film having a large area, passage of a current to a plurality of randomly generated leakage portions is necessary so that it is required to increase a reverse bias voltage to be applied. However, when the reverse bias voltage is increased, there arises the problem that a large current passes to a leakage portion existing in the vicinity of a contact point between a probe and an electrode for applying a voltage, so that pinholes are expanded due to generation of a large amount of heat, or a voltage exceeding a withstand voltage is applied to a normal portion, leading to breakage of an element.
Thus, when a reverse bias voltage is applied to a thin-film photoelectric conversion device to eliminate leakage, a semiconductor thin-film is divided into small-area regions, and the reverse bias voltage is applied to each of the small-area regions. For example, in Patent Document 1, a stacked cell of an amorphous silicon photoelectric conversion unit (top cell) and a microcrystalline silicon photoelectric conversion unit (bottom cell) is divided into a plurality of small-area cells, and a reverse bias voltage is applied to a multi-junction photoelectric conversion device obtained by integrating the plurality of cells into a serial array so that leakage is removed.
In a multi-junction photoelectric conversion device in which a plurality of photoelectric conversion units are stacked, generally leakage portions of the top cell and the bottom cell do not coincide with each other, and thus elimination of leakage by application of a reverse bias voltage tends to be difficult. For example, even when a reverse bias voltage is applied for eliminating leakage existing in the top cell of the multi-junction photoelectric conversion device, the bottom cell behaves as a resistor, and therefore in application of such a reverse bias voltage within a range where an element is not broken, passage of an amount of current sufficient to insulate leakage portions is difficult.
Patent Document 1 suggests a method in which leakage in a plurality of cells is sequentially eliminated by selectively feeding a reverse bias current into a cell to be subjected to elimination of leakage in a state in which cells other than the cell to be subjected to elimination of leakage are irradiated with light to generate a photocurrent. For example, when leakage in an amorphous silicon thin-film of a top cell in a specific small-area region is eliminated, the target small-area region is irradiated with long-wavelength light that can be absorbed by microcrystalline silicon of a bottom cell while other small-area regions are irradiated with light in a wide wavelength range, so that a photocurrent is generated in cells other than the top cell in the target small-area region. When a reverse bias voltage is applied in this state, a reverse bias current selectively passes into a leakage portion of the target small-area region, so that leakage can be eliminated. When a reverse bias voltage is then applied with a photocurrent generated in cells other than the bottom cell by irradiating the target small-area region with short-wavelength light that can be absorbed by amorphous silicon, leakage in the top cell can be eliminated.